服务器之家

服务器之家 > 正文

R语言中for循环的并行处理方式

时间:2022-01-11 15:33     来源/作者:SANGF

前言

本文用于记录笔者在将R语言中的for语句并行化处理中的一些问题。

实验

这里使用foreach和doParallel包提供的函数实现for语句的并行处理。

for语句脚本

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
func <- function(x, y, z) {
  return(x^y/z)
}
# >>> main <<<
x <- 2
y <- 3
z <- 1:100000
start <- (proc.time())[3][[1]]
a <- 0
for (i_z in z) {
  a <- a + func(x, y, i_z)
}
end <- (proc.time())[3][[1]]
print(paste('Result = ', round(a, 2), ', time = ', (end-start), 's', sep=''))

输出:

[1] "Result = 96.72, time = 0.177s"

并行化版本

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
library(foreach)
library(doParallel)
func <- function(x, y, z) {
  return(x^y/z)
}
# >>> main <<<
x <- 2
y <- 3
z <- 1:100000
start <- (proc.time())[3][[1]]
cl <- makeCluster(12)
registerDoParallel(cl)
a <- foreach(z=z, .combine='rbind') %dopar% func(x, y, z)
a <- sum(a)
stopCluster(cl)
end <- (proc.time())[3][[1]]
print(paste('Result = ', round(a, 2), ', time = ', (end-start), 's', sep=''))

输出:

[1] "Result = 96.72, time = 37.988s"

总结

1、这里发现并行化所用时间大于非并行化所用过的时间,是因为需要执行的操作(func函数)过于简单,而foreach处理时会有额外的资源消耗。此时foreach额外消耗的资源远大于需要执行的操作所需的资源,因此会导致并行化后反而使用的时间增加了。所以对于一些复杂的操作比较适合使用并行化的策略。

2、foreach函数的.packages参数可以为并行化函数传递额外需要的包。

3、foreach中的参数为需要在func中循环的变量,其他固定的变量则在func中传入。参数可以是data.frame类型。

补充:R语言--for循环语句的使用

R语言for循坏语句的使用(多个for)

对于多个for循还语句,R语言的执行顺序(以3个for为例):从外向内单个执行,里边循还完整,再往外一层,直到全部完成。话不多说,上例子:

代码:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
library(data.table)
mm<-data.table()
m<-c(1,2,3,4,5)
n<-c('a','b','c','d','e')
o<-c(6,7,8,9,10)
for (i1 in m){
  for ( i2 in n){
     for (i3 in o){
       print(c(i1,i2,i3))
       aa<-data.table(i1,i2,i3)
       bb<-rbind(mm,aa)
       
     }
  }
}

执行结果:

?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
[1] "1" "a" "6"
[1] "1" "a" "7"
[1] "1" "a" "8"
[1] "1" "a" "9"
[1] "1"  "a"  "10"
[1] "1" "b" "6"
[1] "1" "b" "7"
[1] "1" "b" "8"
[1] "1" "b" "9"
[1] "1"  "b"  "10"
[1] "1" "c" "6"
[1] "1" "c" "7"
[1] "1" "c" "8"
[1] "1" "c" "9"
[1] "1"  "c"  "10"
[1] "1" "d" "6"
[1] "1" "d" "7"
[1] "1" "d" "8"
[1] "1" "d" "9"
[1] "1"  "d"  "10"
[1] "1" "e" "6"
[1] "1" "e" "7"
[1] "1" "e" "8"
[1] "1" "e" "9"
[1] "1"  "e"  "10"
[1] "2" "a" "6"
[1] "2" "a" "7"
[1] "2" "a" "8"
[1] "2" "a" "9"
[1] "2"  "a"  "10"
[1] "2" "b" "6"
[1] "2" "b" "7"
[1] "2" "b" "8"
[1] "2" "b" "9"
[1] "2"  "b"  "10"
[1] "2" "c" "6"
[1] "2" "c" "7"
[1] "2" "c" "8"
[1] "2" "c" "9"
[1] "2"  "c"  "10"
[1] "2" "d" "6"
[1] "2" "d" "7"
[1] "2" "d" "8"
[1] "2" "d" "9"
[1] "2"  "d"  "10"
[1] "2" "e" "6"
[1] "2" "e" "7"
[1] "2" "e" "8"
[1] "2" "e" "9"
[1] "2"  "e"  "10"
[1] "3" "a" "6"
[1] "3" "a" "7"
[1] "3" "a" "8"
[1] "3" "a" "9"
[1] "3"  "a"  "10"
[1] "3" "b" "6"
[1] "3" "b" "7"
[1] "3" "b" "8"
[1] "3" "b" "9"
[1] "3"  "b"  "10"
[1] "3" "c" "6"
[1] "3" "c" "7"
[1] "3" "c" "8"
[1] "3" "c" "9"
[1] "3"  "c"  "10"
[1] "3" "d" "6"
[1] "3" "d" "7"
[1] "3" "d" "8"
[1] "3" "d" "9"
[1] "3"  "d"  "10"
[1] "3" "e" "6"
[1] "3" "e" "7"
[1] "3" "e" "8"
[1] "3" "e" "9"
[1] "3"  "e"  "10"
[1] "4" "a" "6"
[1] "4" "a" "7"
[1] "4" "a" "8"
[1] "4" "a" "9"
[1] "4"  "a"  "10"
[1] "4" "b" "6"
[1] "4" "b" "7"
[1] "4" "b" "8"
[1] "4" "b" "9"
[1] "4"  "b"  "10"
[1] "4" "c" "6"
[1] "4" "c" "7"
[1] "4" "c" "8"
[1] "4" "c" "9"
[1] "4"  "c"  "10"
[1] "4" "d" "6"
[1] "4" "d" "7"
[1] "4" "d" "8"
[1] "4" "d" "9"
[1] "4"  "d"  "10"
[1] "4" "e" "6"
[1] "4" "e" "7"
[1] "4" "e" "8"
[1] "4" "e" "9"
[1] "4"  "e"  "10"
[1] "5" "a" "6"
[1] "5" "a" "7"
[1] "5" "a" "8"
[1] "5" "a" "9"
[1] "5"  "a"  "10"
[1] "5" "b" "6"
[1] "5" "b" "7"
[1] "5" "b" "8"
[1] "5" "b" "9"
[1] "5"  "b"  "10"
[1] "5" "c" "6"
[1] "5" "c" "7"
[1] "5" "c" "8"
[1] "5" "c" "9"
[1] "5"  "c"  "10"
[1] "5" "d" "6"
[1] "5" "d" "7"
[1] "5" "d" "8"
[1] "5" "d" "9"
[1] "5"  "d"  "10"
[1] "5" "e" "6"
[1] "5" "e" "7"
[1] "5" "e" "8"
[1] "5" "e" "9"
[1] "5"  "e"  "10"

以上为个人经验,希望能给大家一个参考,也希望大家多多支持服务器之家。如有错误或未考虑完全的地方,望不吝赐教。

原文链接:https://www.cnblogs.com/sangf/p/14336269.html

标签:

相关文章

热门资讯

蜘蛛侠3英雄无归3正片免费播放 蜘蛛侠3在线观看免费高清完整
蜘蛛侠3英雄无归3正片免费播放 蜘蛛侠3在线观看免费高清完整 2021-08-24
yue是什么意思 网络流行语yue了是什么梗
yue是什么意思 网络流行语yue了是什么梗 2020-10-11
背刺什么意思 网络词语背刺是什么梗
背刺什么意思 网络词语背刺是什么梗 2020-05-22
2020微信伤感网名听哭了 让对方看到心疼的伤感网名大全
2020微信伤感网名听哭了 让对方看到心疼的伤感网名大全 2019-12-26
2021年耽改剧名单 2021要播出的59部耽改剧列表
2021年耽改剧名单 2021要播出的59部耽改剧列表 2021-03-05
返回顶部